1. Field of the Invention
The present invention relates to a particle counter, and more particularly to a particle counter capable of counting a number concentration of ultrafine particles by condensing a vaporized working liquid on the surfaces of ultrafine particles to grow them, charging ions on the grown micro particles and then measuring an amount of the ions.
2. Description of the Prior Art
In recent years, it has been very important to measure a number concentration of ultrafine particles when closely examining phenomena of photochemical smog, visibility, atmospheric chemical reaction and the like or evaluating an toxicity of ultrafine particles deeply inhaled in human lungs through a breathing, in fields of atmospheric environments. In addition, the importance of the measurement is further emphasized in a variety of industrial applications such as analysis of physicochemical properties of ultrafine particles, semiconductor field, particle control of nano-industry field and the like.
An equipment of measuring a number concentration of particulate matters including ultrafine particles may be classified into an equipment of using an optical sensor to measure the number of particles and an equipment of charging particles to measure a current.
The equipment using the optical sensor includes a wide range particle spectrometer (WPS) available from MSP company, a condensation nucleus counter (CNC) of Met One company, a condensation particle counter (CPC) constituting a scanning mobility particle sizer (SMPS) of TSI company, a laser particle counter (LPC) available from PMS company and the like. In addition, the equipment using the electrical measuring method includes, for example an electrical low pressure impactor (ELPI) available from Dekati company.
The CPC of TSI company widely used among the equipments using the optical sensor for measurement vaporizes alcohol, condenses the vaporized alcohol on surfaces of ultrafine particles to enlarge the particles and then optically measures a number concentration of the particles. However, the equipments using the optical sensor to measure the number concentration of ultrafine particles, including the CPC, are very expensive and the optical sensor is liable to be contaminated by working liquid while they are moved to other measurement places.
In addition, the ELPI using the electrical method charges wide-range particles to the utmost and then measures charge quantity of the charged particles, thereby measuring the number concentration of the particles. In this case, the maximal charge quantity capable of being retained by the particle is determined by a size of the particle. Although a spherical particle having a diameter of 1 μm can contain approximately 156,000 electrons, the charge quantity is highly different depending on methods of charging the particles. In general, when a number concentration of the particles uniformly charged with about 1,000 charges is 100 particles/cm3 and a flow rate of 1 l/min is allowed to pass through an ammeter, i.e., 1×105 particles per minute pass through an ammeter, a current to be detected is about 2.7×1031 13 A. Accordingly, the measured current can be transformed into a number concentration of the particles.
When such electrical method is used, there is not occurred the contamination problem as for the optical sensor during the movement. However, since a lower limit of measurable particle is about 0.03 μm, it is possible to measure only a particle having a relatively large diameter compared to the equipment using the optical sensor. The reason is that since the smaller the size of the particle, the less the charge quantity charged to the surface of the particle, there is limitation in a measurable low electric signal. Accordingly, the electrical measurement of a number concentration of particles has disadvantage in accuracy, compared to the equipment using the optical sensor.